1. Field of the Invention
This invention relates to balloons for catheter devices adapted to be used for angioplasty and/or valvuloplasty and, more particularly, to balloons having stiffening means to maintain the shape of the balloon when in the expanded state.
2. Description of the Prior Art
Inflatable balloons are presently employed to dilate stenotic arteries (angioplasty) and to dilate stenotic cardiac valves (valvuloplasty). In these procedures, considerable force must be generated to dilate these stenotic arteries and valves, particularly if these arteries and/or valves are heavily ingrown with scar tissue or if they are calcified. Hence, the balloons used for these procedures are filled with liquid under high pressure, often as high as 5 atmospheres (75 p.s.i.).
Despite the use of such high pressures, dilation with these balloons may be less than desired and may not be adequate. One reason for this inadequacy is related to the irregularity of the stenotic structure on which the angioplasty or valvuloplasty procedure is being performed. When the expanded balloon impinges on a local elevation, the elevation will distort the balloon which results in a very limited area of the balloon contacting the local point of irregularity or elevation and thereby greatly reducing the force that can be exerted by the contacting surface of the balloon on the irregular shape. For example, if a local irregularity is one-eighth inch by one-eighth inch at its point of highest elevation, the area of such elevation is one-sixty-fourth square inches. An internal pressure of 75 p.s.i. from the balloon on this area provides a force barely more than one pound. Such a force may be far less than that required to dilate the stenotic orifice of an artery or valve.
Presently this problem is largely unsolved since the ability of balloons to accept higher pressure is compromised by the limitation on the thickness of their skin in order to minimize their bulk so as to enable them to be inserted into the vascular system.
Balloon catheters with stiffeners have been constructed, but they do not address, let alone solve, the problems discussed above. Three patents dealing with stiffened balloons are:
Baskin--U.S. Pat. No. 2,854,983 PA1 Valli--U.S. Pat. No. 4,437,856 PA1 Rowe--U.S. Pat. No. 2,078,686
Rowe, U.S. Pat. No. 2,078,686, shows a ribbed support surrounded by an inflatable balloon. The ribs do not inflate with the balloon.
Baskin, U.S. Pat. No. 2,854,983, shows a catheter employing an inflatable bag 24. The bag has strips 46 attached thereto. Inflation of the bag serves to "expand" the strips. This serves in turn to keep the area open for drainage. The strips, however, are totally unsuitable and are not intended to augment the stiffness of the contacting surfaces for the expanded balloon, nor to deliver any expansile or dilating forces upon expansion of the balloon.
Valli, U.S. Pat. No. 4,437,856, teaches a dialysis catheter which employs an inflatable portion and a rib structure, which ribs serve as passages for the dialysis fluid, alternatively as collectors for the returning fluid, and alternatively as unperforated supports.